1. Field of the Invention
The present invention relates to a low melting point frit paste composition, and more particularly, to a low melting point frit paste composition which is sealable and appropriate for manufacturing a flat panel, protects an element weak to heat and improves a process yield with good print properties, and a sealing method for an electric element using the same.
2. Description of the Related Art
There have been considerable studies about OLEDs in recent years as they can potentially apply to various arear and electroluminescent devices. For example, an OLED can be used in manufacturing a panel thinner than existing display panels. Also, the OLED provides good process availability and has drawn attention as a next generation display with process appropriateness of a flexible display as a next generation display. The OLED display has good contrast and a wide viewing angle, high brightness and low driving voltage and is light.
However, the OLED display can easily deteriorate by responding to oxygen and moisture in the OLED display. Thus, dark spot and pixel shrinkage occur and yield is lowered.
To address such a problem, various types of sealing materials are being developed. The sealing materials include photo-curing, thermosetting resin composition, sealing technique by vapor deposition, etc., which can be found in various documents. However, such sealing materials are not good enough to protect the OLED element and secure stability and life, causing difficulties to manufacture the OLED element.
It is well known that the life of the OLED display can sharply increase if electrodes and organic layers in the OLED display are tightly sealed from the surrounding environment. However, several factors hinder the correct sealing of the OLED display. Some of those factors will be briefly described. First, a tight sealing should have a barrier to oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day). The size of the tight sealing should be as minimum as possible (e.g., <2 mm) not to affect the size of the OLED display. Also, the temperatures generated during the sealing process should not damage materials (e.g., electrodes and organic layers) within the OLED display. For example, a first pixel of the OLED which is 1 to 2 mm far from the OLED display sealing should not be heated over 100° C. during the sealing process. Gas which is emitted during the sealing process should not contaminate materials within the OLED display. Moreover, an electric connector (e.g., thin film chromium) should be placed within the OLED display for the tight sealing.
A general method of sealing the OLED display is to use epoxide, inorganic and/or organic materials forming the sealing after being processed with UV.
Vitex System manufactures a coating agent named Barix™, which can be used to seal the OLED display with the inorganic and organic materials. Such a sealing method provides good physical intensity while it may not be cost effective since the process expense is very high. Also, diffusion of oxygen and moisture to the OLED display is not prevented. Another method of sealing the OLED display is to use metal welding and soldering. In this case, there is a substantial difference between CTEs of a glass plate and metal in the OLED display, thereby failing to provide durability at a wide range of temperatures. Thus, if the sealing method is used in a wider display, yield of the panel is lowered and errors increases due to a twist and cracks after the sealing process. Recently, a low melting point frit paste composition which can be used for the tight sealing by laser emission has been developed and used in sealing the OLED. However, if this paste composition applies to a dispensing process, it is hardly thin and processing time is extended, thereby adversely affecting productivity. If the paste composition applies to a screen printing, printing properties are ununiform and yield of the panel is lowered after the sealing process.
To perform a thin film process, one of strengths of the OLED, the thickness of the sealing material should be minimized. Thus, it is essential to apply a sealing material to as much thin film as possible by using the screen printing. However, a thin film process of about 10 μm is not possible for applying a paste to the dispensing process. In case of screen printing, errors occur during the sealing process due to ununiform patterns after printing and firing processes to thereby sharply decrease yield. To address such a problem, a composition including additives such as a dispersant, a leveling agent, an antifoaming agent, etc. has been developed. However, such additives contaminate the OLED during the sealing process, and act as impurities while a frit paste is densified. Thus, the additives are not appropriate as sealing materials sealing the OLED element.
Thus, there have been continuous demands for addressing the problems related to the typical sealing and sealing method for the OLED display.